[accelerator] fix preview UX on mobile when there is an error/warning

frontend/src/app/shared/components/mempool-error/mempool-error.component.html

@@ -1,2 +1,2 @@
-<div class="alert alert-danger" [innerHTML]="errorContent">
+<div class="alert" [class]="alertClass" [innerHTML]="errorContent">
 </div>

frontend/src/app/shared/components/mempool-error/mempool-error.component.ts

@@ -33,6 +33,7 @@ export function isMempoolError(error: string) {
 })
 export class MempoolErrorComponent implements OnInit {
   @Input() error: string;
+  @Input() alertClass = 'alert-danger';
   errorContent: SafeHtml;
 
   constructor(private sanitizer: DomSanitizer) { }